The present invention relates to structural adhesives and more particularly to an improved rubber-modified epoxy adhesive and method of making the same for use in repairing damaged areas of graphite-epoxy composite structures.
In the construction of today's aircraft, particularly those of the military, an increasing amount of advanced composite materials are being utilized to produce relatively strong, lightweight structural members. Most typically having an epoxy resin base impregnated with graphite fibers, these advanced composite materials and the structural members fabricated thereof develop damaged areas during flight operations and routine flight service that require immediate repair. The quick, effective repair of such damaged areas is of critical importance to the safe operation of the aircraft and as a result, the development of reliable measures of repairing the damaged composite structure has become an essential area of concern.
One current method of repair is the adhesive bonding of a patch of the graphite-epoxy composite material over the damaged area. While this method of patch-bonding has had some promising results, there remains a need for developing and selecting an adhesive to make such patch-bonding repairs with higher strength and greater ease. Epoxy film adhesives used initially to fabricate the composite structures have been relatively successful. However, these film adhesives have required refrigerated storage to avoid premature curing, and in those field locations most typically performing patch-bonding repairs, such as on board aircraft carriers, such refrigerated storage has been difficult to provide. Furthermore, because of working space limitations at these field locations, constraints have been placed on the time, temperature, and pressure conditions for adhesive cure.